From the Best Practices for Accepting Payment Cards Article

Large Transactions

Square merchants start off with a per transaction limit of $50,000. If you have general questions regarding large transactions, contact us.

If you would like to accept individual transactions above $50,000 each, you'll need to split the payment into multiple installments. Make sure to record of the receipt number and the total amount charged for each installment. Please note that in order to ensure a secure purchasing environment, we may periodically reach out to customers for additional information regarding their business or transactions.  

Note: Merchants who process more than $100,000 annually will be asked to sign a Commercial Entity Agreement, acknowledging that the payments processed are associated with a commercial business.