Can I put a 4 month old baby in a portable cot for 2 nights while in our care? Thank you!

Red Nose recommends that you only use a portacot that meets the Mandatory Australian Standards (AS/NZS:2195)
Only use the firm, thin, well-fitting mattress that is supplied with the portable cot. Never add a second mattress or additional padding under or over the mattress, which has been specifically designed for the portacot, as baby may become trapped face down in gaps between the mattress and the sides.

If you are accepting a second hand portable cot, look for a label or sticker that says that it complies with the mandatory standard; never place baby in a cot or portable cot that does not definitely meet the current Australian safety standard.
Wear and tear can expose baby to hazards. Only use a portable cot that has the mesh intact and that has no broken parts. Ensure that the base is flat and regularly check the portacot for signs of damage.
https://rednose.org.au/article/portable-cots

Product Safety Australia, who develop & monitor safety standards in Australia, has the following information about Portacots
Folding cots are designed for temporary use. They are also known as portable cots, travel cots or portacots because they are easily collapsible for transport.

Folding cots should only be used as temporary sleeping facilities. They are not suitable for long term sleeping arrangements (no more than a few days). These cots are subject to more wear and tear due to folding and are generally less robust than permanent sleeping enclosures such as household cots.
https://www.productsafety.gov.au/products/babies-kids/kids-furniture/folding-cots
https://www.productsafety.gov.au/standards/folding-cots