From
https://www.avalara.com/us/en/blog/...ection-requirements-for-in-state-sellers.html
New requirements for out-of-state sellers
The new requirements for remote sellers are equally complex. Under the state’s new economic nexus policy, remote sellers must collect and remit Colorado sales tax if, in the previous or current calendar year, they have:
- $100,000 or more of gross sales or services delivered in Colorado, including exempt sales; or
- 200 or more transactions selling tangible personal property or services delivered in Colorado
What this means for out-of-state sellers. Affected
out-of-state retailers must apply for a Colorado sales tax license by November 30, 2018, and commence collecting Colorado state sales tax starting December 1.
Out-of-state sellers will also need to collect and remit applicable local and special district sales taxes that are state-collected.
Like in-state retailers, out-of-state retailers that are required to collect will need to add non-physical locations to their Colorado sales tax accounts. The Department of Revenue recommends doing this sooner rather than later: "Do not wait until the last minute to add non-physical locations. Processing of new sites may take longer than usual to process during peak hours."
Out-of-state retailers whose sales into Colorado are below the threshold may elect to collect and remit Colorado sales tax or they may continue to collect and remit the retailer's use tax. However, those whose sales surpass the threshold must obtain a sales tax license and begin collecting sales tax. If they already have an account with the state, they should add sales tax to their existing account and close their retailer's use tax accounts.