Whenever i do Trade/Loan it pops up with this message

While creating this trade, the offered pokemon(s) of the trade was not found in the player(s) boxes and so the trade was not created successfully.

we checked the TL it was fine and we checked and the pokemon was not NFT but it still gave the same message.

Please Help fix this error

Even though it states your Level Cap as 500 when your Trainer Level is below 500, it seems that your Trainer Level is always your Cap when trading until you reach a Trainer Level of 9,999.
However, if you are trading the Pokemon, not loaning, I believe you can send the Pokemon.