After calls dropped dozens of times I finally got through to a postal worker and she admitted that Posh sellers have been blowing up their lines today and they had NO CLUE of the update!

Poshmark has promised the following (I highlighted the important bits) https://blog.poshmark.com/ :

Poshmark has partnered with USPS to provide complimentary Ground Advantage shipping supplies exclusively for Poshmark sellers. Packaging options include a variety of polymailers, padded mailers, and boxes*.* 
To order your packaging supplies, please call 800-610-8734. Please note that you will need to provide your closet name to USPS to confirm you are a Poshmark seller.

Rest assured, USPS is prepared for this transition and ready to support requests from our community.

I particularly love the last line about USPS being prepared for this (REST ASSURED - ha!)!

I found out that the USPS customer service reps have an internal chat group where they can reach out to each other to help with information about things they are getting calls on and the supervisors and team were all in the dark on this.

Call lines are open M-F 7am - 11pm (1-800-610-8734). Lets help each other out and report back if anyone has any success getting the free packaging Poshmark is promising. Otherwise, this means the discounted shipping makes selling MORE EXPENSIVE because we are now providing shipping materials from our own pockets.

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10:15pm EST Update - Finally got through and the phone system seems to have been fixed to not drop calls since the prompts seemed to be different. The rep said they have been overloaded by Posh sellers but they are working through to get to everyone quickly.

Supplies options includes different polymailers, bubble mailers and boxes. Limited selection but its better than nothing.

I asked what they do with our closet info and she said they are supposed to look us up to verify that we have a closet.

I said that the Posh community is generally really great and that I hoped everyone was being nice and patient with them and she said yes, most were lovely. SOOOO ---- lets represent our community well and let them know how appreciative we are of what they do to support us in our sales!

Got through to USPS (800-610-8734)

The representative I spoke to was well aware of the free "ground advantage" boxes and mailers. All the following come in packs of 25. I was able to order 75 of each box and 100 of the mailers. If you need more, you can, that's just how much I wanted to start off with.

Box 1: 12 x 12 x 8.5

Box 2: 14 x 7 x 5

Poly Padded Bubble Bag: 12.5 x 9.5

Paper Padded: 14.5 x 20,5

Polybag: 14 x 17

I was told it would take 7-10 days to arrive.

Of course, they will ask you for your Poshmark closet name. Hope this helps! I was hung up on about 10 times, and finally on hold for about 30 minutes, and had a very helpful and pleasant representative.

And according to the following link on usps website, ground advantage is eligible for free pickup

https://faq.usps.com/s/article/What-is-Package-Pickup#eligibility

I'm just a poshmark beginner seller and I've never bought anything on Poshmark. I have made a few first sales lately, so this sounds a bit too late i think. First, i read poshmark's shipping guidelines carefully and did as they said, and they mentioned that USPS boxes are free? However, when I went to my local USPS, they always gave me the thin envelopes, which fortunately i can still stuff in the the items (mini backpack, shoes, etc.). I asked but that were the only thing that they gave me, they didn't tell me if I can take the boxes? What if I have to ship bulkier items, like coat or bigger boots? Do I have to buy boxes or should I contact poshmark for helping with packaging? I looked at those boxes (which fits poshmark's requirements) sold at USPS and even the small one were already more than $10, which is what i earned from my sale. Did I forget something? I'm a foreigner so i dont know how USPS works much, j just do what was instructed.

Can I use a medium flat rate box to ship something?