Only Other steam user had a steamwebhelper issue while they try buy something, if this is related to you, you still need to contact steam support only they have insight knowledge on that topic.

I doubt any clear cache or delete it could or should have impact on buy transactions.
and this is among you and steam and bank/credit card company, no steam users advice imo
should help from client,

You can try a from browser, and if taht work, only confirm steam own issue, with it. and you and creditcard company.

We have seen this before on event sale some could use own browser and buy games or transfer to wallet in your case.

imo you still need to make ticket, because this will not go away before they know about it.

Thank you for your answer.

i made a ticket but problem is solved . i switched from beta build to classic and it works. looks like the bug comes from steam beta build.