The JPG format has a pixel size limit of 65,535 x 65,535 pixels. Photoshop however limits JPGs and most formats to 30,000 x 30,000 pixels.
For any images larger than 30,000 x 30,000 pixels you are stuck with the PSB, RAW or TIFF formats, there's no way around that.
From Photoshop Help / Saving Images:
Photoshop supports documents up to 300,000 pixels in either dimension and offers three file formats for saving documents with images having more than 30,000 pixels in either dimension. Keep in mind that most other applications, including versions of Photoshop earlier than Photoshop CS, cannot handle files larger than 2 GB or images exceeding 30,000 pixels in either dimension.
A 180cm x 900cm image at 300PPI is 21,260 x 106,299 pixels. Which is way too big to save as a JPG and I suspect bigger than you need.
For more realistic printing dimensions, read through this related Q&A:
I need to print an image at a certain size. What dimensions and resolution should I use?
If you really need a JPG at that size and resolution you will need to break the image in to smaller sections, but I suspect you can probably work at a lower resolution.