Hi Kim,

Here the connected callback will fire before the wire adapter. So obiviously the account number will be Null.

To overcome this instead of connected callback. Add all the Account Number and Revenue logic checks in new JS method and then invoke this method inside wire adapter result. 

Also debug the account number whether you are null or something else.

Please refer the below code :

import { LightningElement, api, track, wire } from 'lwc';
import { NavigationMixin } from 'lightning/navigation';
import getAccounts from '@salesforce/apex/accountAura.getAccounts';
import { encodeDefaultFieldValues } from 'lightning/pageReferenceUtils';
import { ShowToastEvent } from 'lightning/platformShowToastEvent';

export default class HelloWorld extends NavigationMixin(LightningElement)  {
    @api recordId;

    @track activeStatus='';
    @track accNumber=0;
    @track accRevenue=0;
    @track error=undefined; 
   
    //accessing fields and assigning them to variables
    @wire(getAccounts, {accountID:'$recordId'})
     wiredRecord(result) {
       
       if (result.data) {
         this.error = undefined;
         
         this.activeStatus = result.data.Active__c;
         this.accNumber = result.data.AccountNumber;
         this.accRevenue=result.data.AnnualRevenue;
         this.checkAccountRevenue();
         
       } else if (result.error) {
         this.error = result.error;
         console.log(result.error);
         this.dispatchEvent(
           new ShowToastEvent({
               title: 'error',
               message: result.error.body.message,
               variant: 'error'
           })
       );     
       }
     }
     
 
     //fire event when user push the button 
    checkAccountRevenue(){

    if (this.accNumber==null)
    {
    this.dispatchEvent(
     new ShowToastEvent({
         title: 'error',
         message: 'Account Number cant be null',
         variant: 'error'
     })
    );  

    return;    
    }  

    else if (this.accRevenue<1000){

    this.dispatchEvent(
     new ShowToastEvent({
         title: 'error',
         message: 'You cant submit because Account Revenue is less than $1,000',
         variant: 'error'
     })
    );  

    return;  


    }

    else { 

       this.navigateToNewContactWithDefaults();

      }

    }
 
     //function with default values
    navigateToNewContactWithDefaults() {
     const defaultValues = encodeDefaultFieldValues({
         AccountNumber: this.accNumber,
         AnnualRevenue: this.accRevenue,
         Active__c: 'Yes'
     });

     console.log(defaultValues);

     this[NavigationMixin.Navigate]({
         type: 'standard__objectPage',
         attributes: {
             objectApiName: 'Account',
             actionName: 'new'
         },
         state: {
             defaultFieldValues: defaultValues
         }
     });
    }
}


Thanks,
Maharajan.C