Visited website on different dates - apa style Ray, B. (2018, June 25). NB-IoT vs. LoRa vs. Sigfox. Retrieved January 4, 2019, from https://www.link-labs.com/blog/nb-iot-vs-lora-vs-sigfox

In the source reference of my paper I refer to a website. I consulted this website for example on various dates. Do I only have to write the last date or each date separately?
From the link you provided I don't think you need to include the retrieval date for the following reasons.
The blog post you link has a publication date.
A blog post in the APA Blog states the following about website dates.

Determining Website Dates
A second source of confusion is that many websites or webpages do not include publication dates. If no date of publication is provided, use the letters n.d. (which stand for “no date”). The copyright date on the website itself should not be used as the publication date for particular content on that site.
If multiple dates are provided, use the most recent date on which the content was changed. For example, if the site says the content was first published in 2010 and last updated on August 6, 2016, then use the date 2016 in the in-text citation and reference list. However, if the site says it was first published in 2010 and last reviewed in July 2016, then use the date 2010 because a review does not imply that any information was changed.

The following 2 guides also indicate to use a retrieval date if info on page is likely to change over time.
From APA Style Website

When a DOI is not available, and a URL is included, do not include retrieval dates unless the source material may change over time (e.g., wikis).

From APA 6th Edition - University of Lincoln guide

When citing sources that you find on the Internet you only need to include a retrieval date if the information you viewed is likely to change over time.  If you reference an article from a wiki, for example, you would want to include a retrieval date because information in a wiki can be subject to a lot of change.