Apple ID won’t work on iMessage

I tried to setup iMessage but it keeps not working. I went into setting and tried to turn on iMessage but it keeps saying, ‘error occurred during activation’. What ERROR occurred? How can I fix it?

Sometimes I am able to get past that and type in my Apple ID email and password. It says, ‘you can receive iMessages to and reply from’. Listed below this is my phone number, but I need it to be my gmail account.

I tried clicking ‘sign in’ but the sign in option disappears adder I press those words. I tried, ‘use other Apple ID’. When I clicked that option it took me to a page that said, ‘Apple ID sign in requested’, which already had my Apple ID email there. But, after I type in my correct password I get a spinning thing at the top right corner of my screen then after a minute the page goes back to the previous one but has a pop up that says, ‘Unable to contact the iMessage server. Try again’.

Please help