This may relate to inadequacy in the documentation as much as any technical flaw.
Running WP 4.9.4 on Godaddy
1. Went to https://oembed.com/#section7 and found New York Times URL’s
2. Went to https://generatewp.com/oembed/ and enter …
Provider format = https://nytimes.com/*
Endpoint URL = https://www.nytimes.com/svc/oembed
Format type = False
3. Clicked Update code and got… item 4 starts below code…
// Register oEmbed providers
function custom_oembed_provider() {

wp_oembed_add_provider( ‘https://nytimes.com/*’, ‘https://www.nytimes.com/svc/oembed’, false );

}
add_action( ‘init’, ‘custom_oembed_provider’ );

4. Clicked save snippet and got … nothing but sign up request
5. Went to the post in Text edit mode, and inserted: https://generatewp.com/snippet/0md9rdy/ …after the post text
6. Went to post in Visual Edit mode, saw a box with php code in it including:
[screenshot not allowed here, so typing part of it] ….#https?://(www.)?generatewp.com/snippet/.*#i’ ….
7. place a link to a NYT article after the above box of code
8. updated draft of post, previewed post, and all that shows is the box of php code and the picture (but NOT a link or preview of article) from the NYT.
9. Either this just plain doesn’t work, or the documentation is incomplete.