It looks like you were not hired for this project and the offer expired. In the future, please do not work on any project until you accept the offer, it's showing on your My Jobs page as an active contract. Please communicate with your client and ask them to send you a new offer.
re: "So i did a paid trial test for a client and i didn't get selected. But he still needs to pay me and he told me to send a payment request and I do not know how to do that! Please if anyone can help me! "
You worked for free.
There is no way for the client to pay you without a contract.
If the client paid you outside of having had an Upwork contract, it would be a violation of Upwork ToS, and you could be suspended or terminated for accepting such a payment.
In order to get paid on Upwork, you need to have a contract in place before you do the work.
There is no way to simply "send a payment request" to a prospective client.
You should probably just let this go.
You should probably consider this a learning experience, and decide that you will never get paid for this "trial test", and that you are okay with that. Because you learned from your experience.
However: If you think that the client is an honest person and not simply a scammer... Then it IS possible for you to send the client a single message:
"Eugene: Thank you for the opportunity to do the paid test. It looks like the current offer is expired. So you can create a new job posting, and you can use the green Hire button to hire me for that contract. After that, you can use the client-side Send Bonus tool to pay me. If you have any questions, feel free to ask your questions here: https://community.upwork.com"