Falha ao enviar um checkout com valor inteiro

Quando utiliza-se o seguinte código:

pg.add_item(id="0001", description="Exemplo", amount=15, quantity=1)

recebo o seguinte erro:

{'code': '11029', 'message': 'Item amount invalid pattern: 15. Must fit the patern: \\d+.\\d{2}'}

Start by locating the implementation of pg.add_item and how its amount argument is formatted before the PagSeguro checkout request. Reproduce the reported case with amount=15, then verify that integer amounts are accepted while the existing two-decimal amount behavior remains valid.

Written by the indexing model from the issue text.