You need to adjust your max limit field based off the number of licenses they selected. You should be able to do this using the CBSubs Fields integration.
I assume you're using CBSubs Options to select the number of licenses. In which case you can use the substitutions it provides to get the amount they selected. You can find the substitution structure in Integrations > Options > Display at the bottom.
So for example [PLAN_OPTS_PRICE] will return the name of the price/duration they selected when using Prices feature. Example as follows.
Integrations > Options > Prices
Name: 1-yr
Regular Price of plan: 50
Regular Validity duration: 1 year
With the above [PLAN_OPTS_PRICE] would return "1-yr". Plan Options have a substitution per-option. Example as follows.
Integrations > Options > Options
Title: Licenses
Name: licenses
Values
1: Value = 1, Label = 1 License, Price: 50
2: Value = 2, Label = 3 License, Price: 100
3: Value = 3, Label = 3 License, Price: 150
With the above [PLAN_OPTS_OPTION_{OPTION_NAME}] would become [PLAN_OPTS_OPTION_LICENSES] since {OPTION_NAME} is replaced by the options name which in this example is "licenses". [PLAN_OPTS_OPTION_LICENSES] would result in returning "1" for example if 1 License was selected.
Now these can all be used in IF substitutions as well. So for example lets set an integer field based off the price being selected in the below example.
Integrations > Options > Prices
Name: 1-license
Regular Price of plan: 50
Regular Validity duration: 1 year
Name: 2-license
Regular Price of plan: 100
Regular Validity duration: 1 year
Name: 3-license
Regular Price of plan: 150
Regular Validity duration: 1 year
Code:
[cb:if PLAN_OPTS_PRICE="1-license"]1[cb:elseif PLAN_OPTS_PRICE="2-license"]2[/cb:elseif][cb:elseif PLAN_OPTS_PRICE="3-license"]3[/cb:elseif][cb:else]0[/cb:else][/cb:if]
This should set the integer field in CBSubs Fields integration usage to 0, 1, 2, or 3 based off the pricing option selected.