Here is a list of common issues and possible solutions (thanks @Howitzer )   Before diving in, its important to note that Destiny and other PSOBB servers are secure and not attempting to infect your PC. The antivirus related issues happen due to the modifications implemented in the game which some antivirus programs may flag as a trojan due to their behavior. This post is still in progress and i will update it every now and then. If any other issues arise, you can contact staff at any time here in Discord or Forum via PM for help 
  I downloaded the Installer but it doesnt work
Before downloading the Installer or starting it, make sure that your antivirus is turned off. Some antivirus programs flag it as a threat, despite being marked as a false positive
The game doesnt launch
After installing the game and before reactivating your antivirus, please add an exception for your PSOBB Destiny folder to your Antivirus and Windows defender whitelist. The path for this is C:-> Program Files -> PSOBB Destiny. See down below how to add exclusions for Windows defender. Also, check your AV quarantine to make sure it hasn't been moved there
How to add PSOBB Destiny folder in exclusions for Windows Defender
Go to Windows > Settings > Privacy and Security > Windows Security > Virus and threat protection > Manage settings > Add or remove Exclusions > add PSOBB Destiny folder there from C:-> Program Files -> PSOBB Destiny
The game opens and closes as soon as I click on 'play' in the launcher
Ensure that you do not surpass your monitor's maximum resolution in the launcher options. If the game resolution exceeds your monitor's maximum, the game will simply open and close. If this doesn't resolve the issue, experiment with different resolutions until you find one that works. this issue asked most. 
 I disconnect randomly and dont know why / Server saying error 903 or full
Try not using a wireless connection unless you have a good router or Please check your connection is stable or not. This is the same with other games as relying on wifi connection can cause issues with connection performance.
I forgot my Username and can't login
We need your Guildcard. You can potentially find it in the chat log folder under C: -> Program Files -> PSOBB Destiny -> Chatlog, or try to find the account verification email. Alternatively, ask a player with whom you have either exchanged GC or DTs. Contact the staff and provide them with this information for help   Client downloads patch data (psobbw.exe) everytime and can't start If you are opening game directly, try to open via launcher. it solves this issue.   If you tried and still have a question, feel free to ask staffs. （もし色々試してもわからない事がある時は気軽に聞いてください）