Pagination Slug Issue
Pagination is for breaking up a list of entries into different pages. p3 means page 3 of entries.

What you're looking for is the ability to link to the next/previous entry. If you are ordering your entries like a blog, by post date, newest first you can create the links like this. On your single entry template:

{% set nextEntry = craft.entries.section('posts')
    .postDate('&gt;= ' ~ entry.postDate.timestamp)
    .order('postDate asc')
    .id('not ' ~ entry.id)
    .one() %}

{% if nextEntry %}
    &lt;a href="{{ nextEntry.url }}"&gt;Next Post&lt;/a&gt;
{% endif %}

{% set previousEntry = craft.entries.section('news')
     .postDate('&lt;= ' ~ entry.postDate.timestamp)
     .order('postDate desc')
     .id('not ' ~ entry.id)
     .one() %}

{% if previousEntry %}
    &lt;a href="{{ previousEntry.url }}"&gt;Previous Post&lt;/a&gt;
{% endif %}


entry is the current entry you're viewing. If you're ordering the entries in a different way you can adjust the queries. This answer goes into more detail, including how to change this if you're ordering by title.

If you have your entries in a structure section you can do this:

{% if entry.getNextSibling() %}
    &lt;a href="{{ entry.getNextSibling().url }}"&gt;Previous Post&lt;/a&gt;
{% endif %}

{% if entry.getPrevSibling() %}
    &lt;a href="{{ entry.getPrevSibling().url }}"&gt;Previous Post&lt;/a&gt;
{% endif %}