Slow loading of products and error

Dear Sirs: It happens that when I go to upload products from AliExpress, the loading takes several minutes (between 5 and 10 for each product) which is not normal. Likewise, several times -not all- I get a red notice that I attach about a 504 error, which prevents uploading many products. I have reviewed all the possible causes that the warning mentions and all are normal except that the “REST API is disabled”, but I have not found instructions on how to edit this API to include it. I really appreciate your support and cooperation.