@wayx Please accept the answer above if it has solved your initial question and ask a separate question for importing RTF to the description.

@DavidEstevez I have quickly created this Newsletter Endpoint module and you can access the source code here: github.com/reshadzazai/M2-Newsletter-Endpoint/tree/main/… You can further improve it as I have created it in a limited time. I have tested the two endpoints and it works fine.

@Manaf P M That is the issue of indexing, your store misses the indexing process. Check your innodb_buffer_pool_size and update it. Check current: SELECT @@innodb_buffer_pool_size/1024/1024/1024; Check how much is needed: SELECT CEILING(Total_InnoDB_Bytes*1.6/POWER(1024,3)) RIBPS FROM (SELECT SUM(data_length+index_length) Total_InnoDB_Bytes FROM information_schema.tables WHERE engine='InnoDB') A; This is how to set it. SET GLOBAL innodb_buffer_pool_size=15032385536;

@bfontaine Because your custom module has that module in sequence in the /etc/module.xml

To place an order pass the billing address same as the shipping address.