Hello Matteo BOdi
New to mysql so if someone more experienced comes go with them.
When the column reaches the upper limit of the data type, the next attempt to generate a sequence number fails. Use the UNSIGNED attribute if possible to allow a greater range. For example, if you use TINYINT, the maximum permissible sequence number is 127. For TINYINT UNSIGNED, the maximum is 255. See Section 11.1.2, “Integer Types (Exact Value) - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT” for the ranges of all the integer types.
https://dev.mysql.com/doc/refman/8.0/en/example-auto-increment.html
the upper limit of the sequence would be tied to the int type used for the auto increment column in short the value that the int type has would be the number of rows the auto increment can generate before it throws an error at you.
heres articles about the problem at hand
https://blog.chapagain.com.np/mysql-auto-increment-integer-limit-exhausted/
https://www.sqlservercentral.com/forums/topic/auto-increment-int-overflow-or-limit-exceeds-possible
Is the postmeta 40 different rows or one row with 40 columns? If its 40 different rows you would have to times that with an average of how many orders you get within a certain time range to see roughly how many years it would take to fill up the auto increment sequence
hope this helps
Zach Ellis