How to enable unitpay digital signature verification?

Question

PHP

There is html layout (Saved in *.php for the script to work), there is a Unitpay payment system, there is a sea of ​​instructions, source codes, and so on. The unitpay support here is simply in despair, and cannot help in any way.
At first I wrote everything manually, for myself, but the digital signature is not transmitted, after that I decided to use the great search for "coal", I found a couple of sources, changed the parameters for myself, I launch it, I get the same thing again. When asked in support, I only receive a link to create a payment (And everyone that I have already done myself, and used the source code, but there’s no point), they advised me to turn off the signature verification, but even there the trouble arises.
Who worked, who faced similar, and how did you solve the problem?