Post-processing apparatus, control method therefor, and non-transitory computer-readable storage medium

A control method for a post-processing apparatus to be connected to an image forming apparatus, the post-processing apparatus including a sheet conveying unit configured to convey a sheet received from the image forming apparatus, a sheet detecting unit, which is arranged in a conveyance path of the sheet conveying unit, and is configured to detect the sheet, and a post-processing unit configured to perform a post-processing on the sheet conveyed by the sheet conveying unit, the control method comprising:

• performing the post-processing on a sheet of a first type in a first post-processing mode;
• performing the post-processing on a sheet of a second type having a light transmittance higher than a light transmittance of the sheet of the first type in a second post-processing mode, which is different from the first post-processing mode in conveyance control of the sheet conveying unit;
• and
• in a case in which a job for performing the post-processing on a sheet of a third type different in type from the sheet of the first type and the sheet of the second type is executed, causing the post-processing apparatus to operate in the second post-processing mode until it is determined whether the sheet of the third type is detectable by the sheet detecting unit, causing the post-processing apparatus to operate in the first post-processing mode when it is determined that the sheet of the third type is detectable by the sheet detecting unit, and causing the post-processing apparatus to operate in the second post-processing mode when it is determined that the sheet of the third type is undetectable by the sheet detecting unit.