What’s wrong with my buyToken function?

Here is my solidity

interface IERC20 {     function decimals() external view returns (uint8);     function totalSupply() external view returns (uint);     function balanceOf(address owner) external view returns (uint);     function allowance(address owner, address spender) external view returns (uint);      function approve(address spender, uint value) external returns (bool);     function transfer(address to, uint value) external returns (bool);     function transferFrom(address from, address to, uint value) external returns (bool); }  interface V2 {     function decimals() external view returns (uint8);     function totalSupply() external view returns (uint);     function balanceOf(address owner) external view returns (uint);     function allowance(address owner, address spender) external view returns (uint);      function approve(address spender, uint value) external returns (bool);     function transfer(address to, uint value) external returns (bool);     function transferFrom(address from, address to, uint value) external returns (bool); }  pragma solidity ^0.5.17; contract tokenSales {     //string public name = "EthSwap Instant Exchange";          // IERC20 public token;     // V2 public rgp;     address token = 0x87e9D87f85e80D79A77067A090F0748241892F74;     address rgp = 0x153Eef8365e8F4ae62aC99b6C84520f81F572827;     address owner;     uint public price;          uint256 public tokensSold;     uint256 public decimals;          event sold(address account, uint price, address token);          modifier onlyOwner() {         require(             msg.sender == owner,             "RGP Token: Caller is not the Owner"         );         _;     }      constructor(uint _price) public payable{         owner ==  msg.sender;         price = _price;           // SMC: 0xDA0bab807633f07f013f94DD0E6A4F96F8742B53     }          function() external payable{         buyTokens();         msg.value;     }      // Guards against integer overflows     function mul(uint x, uint y) public pure returns (uint z) {         require(y == 0 || (z = x * y) / y == x, 'ds-math-mul-overflow');     }                  //uint tokens = contribution.mul(multiplier).div(TOKEN_PRICE);         //tokenAllocations[investor] = tokenAllocations[investor].add(tokens);         //tokensSold = tokensSold.add(tokens);          function setBUSDCPrice(uint _price) public onlyOwner {         price = _price;     }          function sendCollectedBUSDC (address payable _recipient)         external         onlyOwner     {         if (address(this).balance > 0) {             _recipient.transfer(address(this).balance);         }     }      function buyTokens() public payable {         //CHECK FOR INPUT BALLANCE         require(msg.value > 0, "RGP: INSUFFICIENT INPUT BALLANCE, YOU NEED TO SEND SOME BUSDT");                  //CALCULATE THE AMOUNT OF TOKEN TO PURCHASE         uint256 tokensToBuy = mul(msg.value, uint256(10) ** IERC20(token).decimals()) / mul(price, uint256(10) ** V2(rgp).decimals());                  //ALLOWANCE FOR BOTH ADDRESS(THIS) AND MSG.SENDER         V2(rgp).allowance(msg.sender, address(this));         IERC20(token).allowance(address(this), msg.sender);                  //REQUIREMENT FOR ALLOWANCE         tokensToBuy <= V2(rgp).allowance(address(this), msg.sender); // "RGP: CHECK THE TOKEN ALLOWANCE OF ADMIN";         msg.value <= IERC20(token).allowance(msg.sender, address(this)); // "RGP: CHECK THE TOKEN BALANCE OF BUYER";                  //APPROVE FOR BOTH MSG.SENDER AND ADDRESS(THIS)         V2(rgp).approve(msg.sender, tokensToBuy);         IERC20(token).approve(address(this), msg.value);                  //TRANSFER FROM MSG.SENDER TO ADDRESS(THIS)         IERC20(token).transferFrom(msg.sender, address(this), msg.value);                  //CHECK FOR BALANCE OF ADMIN         uint256 rgpBalance = V2(rgp).balanceOf(address(this));                  //REQUIRE THAT THE BALANCE APPROVED IS GREATER THAN THE TOKENS TO BUY.         require(rgpBalance >= tokensToBuy, "RGP: NOT ENOUGH TOKEN IN THE RESERVE");                  //TRANSFER FROM RGP TO MSG.SENDER         V2(rgp).transferFrom(address(this), msg.sender, tokensToBuy);                  //REDUCE THE ALLOWANCE OF BOTH PARTIES         IERC20(token).allowance(msg.sender, address(this)) + msg.value;         V2(rgp).allowance(address(this), msg.sender) + tokensToBuy;                  //INCREASE THE ALLOWANCE OF BOTH PARTIES.         IERC20(token).allowance(msg.sender, address(this)) + msg.value;         V2(rgp).allowance(address(this), msg.sender) + tokensToBuy;                 //          tokensSold += msg.value;          emit sold(msg.sender, msg.value * price, address(token));              }      function endSale() public onlyOwner{             // Send unsold tokens to the owner.         require(V2(rgp).transfer(owner, address(this).balance), "RGP: Sales ended.");         require(IERC20(token).transfer(owner, address(this).balance), "RGP: Sales ended.");              msg.sender.transfer(address(this).balance);     } } 

Deployed to ropsten "HERE"

The token address "TOKEN ADDRESS".

Please I have been on this for some days trying to figure out what wrong but I couldn’t I have checked related issues on this platform and others still the same, I actually taught it was stress so I decided to take some time out and came back still can’t figure it out.

I test on remix it deducts ether from msg.sender and did not credit to smart contract address and as well msg.sender did not receive token.