You are responsible for obtaining all the necessary documents to enter the country you are traveling to, including the visa.
Remember that each country has particular visa requirements that vary depending on the traveler’s nationality. Be sure to check your Embassy's website for detailed information.
Once you get to the airport or the immigration counter, you will probably be requested to show your Confirmation Voucher (which you receive by email when you confirm your trip on the platform) and/or other travel/administrative documents. It is your responsibility to make sure you have all the necessary documents in hand at the time of your travel.
Check this site out for more info.
It's very important to keep in mind that Worldpackers is a platform that promotes cultural exchanges, not job opportunities.
In other words, you are going to a foreign destination to better understand its culture and to learn and collaborate with the locals. Your host will help you have an unforgettable experience, providing you with accommodation while you offer them help with daily routines.
Make sure anyone who asks you understands this so as to avoid having issues with the immigration department and enjoy every single day of your trip! :-)