The IRS says:

Payment Status Not Available:

If you get this message, either we have not yet processed your payment, or you are not eligible for a payment. We will continue to send the 2021 Economic Impact Payment to eligible individuals throughout 2021.

Need More Information:

If you get this message, your payment was returned to the IRS because the post office was unable to deliver it.

To have your payment reissued as a direct deposit, you can provide a routing and account number for a:

• Bank account
• Prepaid debit card (must be reloadable; contact the card issuer for information)
• Alternative financial products that have a routing and account number associated with them

If you don’t provide account information, we can’t reissue your payment until your address if updated. See My address has changed or is incorrect. What can I do to change or correct it to receive my payment?

The above is an extract of this IRS FAQ.

Trying to apply for it

So what I have to get the 3rd stimulus check 

Do I have to apply again through your system to receive it.That the message I received when I check it. Im on disability 

My address is correct

You don't need to do anything.  It will be automatic.  This information is provided by the IRS - Third Stimulus FAQ 

How do I apply for it?

If you received the first and second payments, the third will be sent to you the same way. 

Below is the IRS link for the third stimulus payment but it might not be updated for everyone yet. 

There is no application process. 

IRS LINK