Thank you! I almost forgot to write the follow-up, whoops!
I ended up asking for help in the modpack’s Discord server and luckily the author himself of the AMP guide I mentioned was willing to take time out of his day to help me in a 1-on-1 call. I greatly appreciate his help as he kindly guided me through every single step in setting up the server and even gave me tips to have it run smoother.
Anyway, turns out the issue was due to me not giving AMP itself enough RAM. I did not know, and therefor learnt, that AMP itself requires a good 2-3GB of memory on its own. The server now runs with only 5GB. Not the greatest- but not terrible.
May consider other hosting options.