I have tried signing up through social media such as Facebook but it still doesn't work. What is the issue here?
You are ineligible to use this service
According to sayat.me 's Terms Of Service You must be at least 18 Years of Age
To accept these Terms on behalf of yourself or on behalf of a legal entity, you must have the legal capacity to do so. This means that if you accept these Terms on behalf of yourself, you must be at least 18 years of age or have valid authorisation from your legal representative. If you accept these Terms on behalf of a legal entity, the legal entity must be duly incorporated and you must have the legal authority to bind that legal entity. By accepting these Terms you confirm the foregoing.
You are 14 and thus cannot legally sign up for this service without valid authorisation from your legal representative. I presume you also signed up for your Facebook/Instagram with your real age, which is why the checks are failing and the server is refusing to sign you up.
This is probably because sayat.me do not want to be held liable in a court if you are bullied or something else happens to you while you use their service.