Contract can be happen verbally also. If there any problem Then how to prove that there was a contract. Ex: if I say I’ll buy your pen for $1 he accepted and if he didn’t how I’m gonna sue him if the contract is verbally.
There will be a problem proving the contract exists unless there is evidence of the agreement. Eg a third party hears it, or there is a recording. Even if no evidence, the contract still exists.