TypeError
TypeError: TransactionRollbackError('could not serialize access due to concurrent update\n',) is not JSON serializable

Traceback (most recent call last)
File "/home/tyrlabx/fe_lite/app.py", line 256, in add_invoice
resp = post_invoice(invoice_created)
File "/home/tyrlabx/fe_lite/app.py", line 201, in post_invoice
Invoice.set_number(invoices)
File "/usr/local/lib/python3.5/dist-packages/trytond/modules/account_invoice/invoice.py", line 1005, in set_number
cls.save(invoices)
File "/usr/local/lib/python3.5/dist-packages/trytond/model/descriptors.py", line 33, in newfunc
return self.func(owner, *args, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/trytond/model/modelstorage.py", line 1557, in save
(([r], save_values[r]) for r in to_write), ()))
File "/usr/local/lib/python3.5/dist-packages/trytond/modules/account_invoice/invoice.py", line 1120, in write
super(Invoice, cls).write(*args)
File "/usr/local/lib/python3.5/dist-packages/trytond/model/modelsql.py", line 147, in wrapper
return func(cls, *args, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/trytond/model/modelsql.py", line 967, in write
where=red_sql))
File "/usr/local/lib/python3.5/dist-packages/trytond/backend/postgresql/database.py", line 65, in execute
cursor.execute(self, sql, args)