Interesting, after 5 months, I received an email from mempool telling I have access to their accelererator.
Me, I've registered since November 29, 2023 and I just received the same email 3 days ago.
Seems like those who got early access are donators and everyone else are granted access only after when they officially released the service.
On a side note, you could've cut cost on the accelerator's payment if you managed to replace the transaction using the given instructions above.