How can I execute the php program of another website in the background while executing a php program?

How can I execute the php program of another website in the background while executing a php program? how can I execute the php program of another website in the background while executing a php program.
After registering A member on website A, I want to insert this data into the member table at the same time on website B (pass username and password in get mode ),
How do I execute the registration program of website B on the background system?

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