If I trade one crypto for another, must I pay tax on the transaction, even if I have no money to pay the tax? Or can I just pay the tax at the time I receive a benefit from a crypto sale?

I am fine paying any tax due once I have received money in my hands for the sale of crypto, but just trading one for another provides me no money to pay the tax. I have not yet received any benefit I can give the government a cut of.