Transaction for a subscription has more than the maximum number of line items

You can't make a change to a subscription that creates a related transaction with more than 100 items.

Error Message	`Subscription update results in a transaction that has more than the maximum number of line items.`
Error Code	`subscription_maximum_number_of_line_items_reached`
Status Code	`400`

Common causes

You're trying to add more than 100 recurring items to a subscription.
You're billing for changes on the next billing period, but there are already line items for previous changes or one-time charges scheduled to be billed on renewal. This results in the next transaction including more than 100 line items.
You're replacing too many recurring items on a subscription in one go, resulting in the next transaction including more than 100 line items.

Solutions

Reduce the number of recurring items on the subscription to 100 or fewer.
Get a subscription including next_transaction to preview line items for the next transaction, including subscription changes and one-time charges that are scheduled to be billed.
Use prorated_immediately or full_immediately as the proration_billing_mode to bill for changes immediately rather than adding them to the transaction created on renewal.