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Why am I not able to reactivate a subscription from a past date?
Solution
The error Reactivation date is incompatible with plan terms will show up when the date which you are trying to Reactivate from doesn't fall under the plan's (say, monthly) billing term ( i.e you can set the reactivate from date only within a month from the current date ). So for example, since the current date is 16th Jan 2020, the Reactivate from date can only be backdated to 16th Dec 2020.
Since invoices can be raised based only on the plan's billing terms (monthly, quarterly, yearly), if the "reactivate from" date is above that billing term, the invoice cannot be created, hence the error.
The only way this can be done is by using the Import Subscription bulk operation and marking the subscription start date to the date which is required. Set the Invoice immediately parameter to True, to raise a charge invoice for the subscription activation.
You can find the mentioned bulk operation under Settings > Import & Export Data > Choose a Bulk operation > Choose Import Subscriptions bulk operation > Download Sample CSV > Mark the above-mentioned parameters as required.
Note: You can make use of Import Subscription API as well - https://apidocs.chargebee.com/docs/api/subscriptions#import_subscription_for_itemsRelated articles and Documentation
How can I reactivate a subscription using the APIs?